Platelet and F-VIII reservoir and phagocytic functions of the spleen have been studied in 7 patients with Hb-S-β-thalassemia and 13 cases of Hb SS disease. Eight splenectomized patients and 11 healthy children served as controls. F-VIII elevation following administration of adrenalin was not found to be a meaningful index in the evaluation of "functional hyposplenism" which was suspected by 99mTc scanning in 42.8 and 77 % of the patients with Hb-S-β-thalassemia and Hb SS disease, respectively. A high platelet count was observed in patients with sickle-cell anemia and Hb-S-β-thalassemia without palpable spleen. The independence of the splenic functions of these patients as emphasized.